We tend to put a lot of effort into ensuring that our seeds germinate, that we plant them out in a suitable place, and that they will create the effect we imagine for our garden. Sometimes, however, the plants take those decisions out of our hands, creating a ‘self-seeding garden’.
I often see red valerian (Centranthus ruber) and Buddlejas that have grown in some remarkable places due to their adaptability, although I’d prefer it if Buddleja wouldn’t grow in my chimney stack. Most of the time, however, if plants end up growing somewhere we’d prefer they didn’t we can just weed them out.
Single and semi-double flowers are more likely to self-seed well than double and fully double flowers, which may well be sterile as the extra petals can be growing in the places where the reproductive parts of the flower would be in single varieties. This can also make double flowers of little value to bees and other pollinating insects as the mutations responsible tend to block access to the nectaries.
In my last garden I grew bronze fennel in a herb bed I’d created in the shell of an old coal bunker. I loved the light and airy fronds waving in the breeze on its tall stems and its dark russet-tinged foliage contrasted with the bright yellow umbels when it flowered.
The next year, fennel plants came up again in the coal bunker, but also in the flower border next to it, by the fence on the south side of my garden. I had to pull up several to keep them under control and stop them shading out the shorter plants at the front of the border.
I’m rather fond of Campanula pyramidalis and I have grown its tall spires of blue bell flowers in the sunny border in my front garden for the past four years, having its flowers in the last three. This year I have four plants in the border where I planted them, with three of them looking likely to flower. I also have campanula plants growing out of the crack at the base of my porch and in the gravel on the path down the side of my house.
The hollyhocks (Alcea rosea) ‘Powder Puffs Mixed’ and the Antirrhinum majus have also self-sown in the border, as have the stocks (Matthiola incana).
These have all self-seeded in a bed against the front wall of my house that catches the sun for most of the day and the evening. The soil is a loam topsoil that I purchased and under it is very sandy. It’s therefore a hot and dry bed that is watered frequently as it gets the run off from the rest of the front garden but is very well drained so never gets waterlogged.
Some plants just seem to lend themselves to self-seeding. Poppies such as Papaver somniferum or P. atlanticum, fennel (Foeniculum vulgare), either bronze or green, and Verbena bonariensis are wonderful and tall, waving in the breeze. Foxgloves (Digitalis Purpurea), Campanula pyramidalis, angelica (Angelica archangelica) and Aquilegia vulgaris can also bring height. These are quite happy in most soils as long as there is good drainage and sun or only partial shade.
For shorter planting or ground cover Geranium pratense, G. macrorrhizum and other cranesbill geraniums, forget-me-not (Myosotis sylvatica), which are happy in similar soil types to the taller plants, Calendula officinalis, nasturtiums (Tropaeolum majus), and cornflower (Centaurea cyanus) which prefer well drained soil and won’t do as well in clay soils.
Self-seeding happens most readily in soils that the plants naturally prefer. It’s their main method of reproduction so it’s what they are evolved to do. Some just do it more readily and easily in our climate. So you’ll generally find that the plants most suited to your soil, level of sun and aspect will self-seed in greater numbers. Just thin out the excess plants, give some away if you can dig them up intact, to keep the balance.
If you wish to encourage plants to self-seed around your garden, pick those that produce a lot of seed (more chances means more likelihood of success) and grow well in the conditions that you have. Improve your soil, if necessary, with compost dug in and remove any weeds before they set seed, to reduce competition for light and nutrients. Leave the seed-heads on the plant to mature and dry and either leave them to disperse naturally or collect the seed and sprinkle it in areas where you have gaps. You can even rake in the seeds or sow them somewhere you have prepared for them if an area needs a kick start.
Using self-seeding plants can be a very cheap and low maintenance way to keep your garden stocked with flowers and it can be exciting to find out just how your garden will look each year when the new plants come up.